Chalcedony
Last updated: April 2026
Microcrystalline quartz aggregate. Generic chalcedony is translucent blue, grey, or white. Varieties include Agate (banded), Carnelian (orange-red), Onyx (black), Chrysoprase (apple-green), and Bloodstone (dark green with red spots) — each listed as a separate entry. RI reads as a single spot (~1.535) due to aggregate structure.
Physical & Optical Properties
RI Range1.530–1.543
SG Range2.58–2.64
SG Typical2.61
Hardness (Mohs)6.5–7
Crystal SystemTrigonal
Optic CharacterAggregate
Dispersion0.013
Fluorescence LWWeak white/cream
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsColorless, Blue Violet, Brown, Multi
SpeciesQuartz
Related: Quartz Varieties
Key Differentiators
- Microcrystalline quartz aggregate — RI ~1.535 lower than macrocrystalline quartz (1.544–1.553)
- Waxy luster (rarely vitreous)
- No facet doubling visible under loupe
- Hardness 6.5–7 — scratches glass
- See specific variety entries: Agate, Carnelian, Onyx, Chrysoprase, Bloodstone
Treatments
- Dyed (very common — carnelian, onyx, chrysoprase)
- Heat Treatment (carnelian brightened from agate)
- Imitation (glass, plastic)
Price Context
Natural — low ($/ct)$1
Natural — high ($/ct)$30
NotePer carat; highly variable by variety — fine chrysoprase and dendritic agate command higher prices; most commercial chalcedony is low cost
Price context is approximate. GemID is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying a chalcedony? GemID walks through these tests in order — RI, SG, fluorescence, and more.
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